RF9 is primarily used in research settings as a potent and selective antagonist of the neuropeptide FF (NPFF) receptors. It is commonly employed in studies aimed at understanding the role of NPFF systems in various physiological processes, such as pain modulation, opioid tolerance, and addiction. Researchers utilize RF9 to investigate its effects on reducing opioid-induced hyperalgesia and enhancing the analgesic properties of opioids. Additionally, it is used in behavioral studies to explore its impact on stress responses and reward pathways, providing insights into potential therapeutic applications for conditions like chronic pain and substance abuse disorders. Its ability to block NPFF receptors makes it a valuable tool in neuroscience and pharmacology research.